1. Field of the Invention
This invention relates to computer systems and more specifically to a battery powered disk drive system connectable to a portable computer.
2. Description of the Prior Art
Many different portable computer systems are available today, most of which comprise the fundamental components as illustrated in FIG. 1. These components include a central processing unit (CPU) 10 which is connected through an input bus 11 to an input module 12 (such as a keyboard), and through an output bus 13 to an output module 14 (typically a display screen). The CPU 10 is also connected through data buses 15 and 16 to at least one memory unit 17.
Memory unit 17 typically stores both computer programs and data. Data in memory unit 17 is processed by CPU 10 in response to the instructions from a computer program being executed in CPU 10.
Memory unit 17 typically includes mass memory 17A, sometimes called secondary memory, and main memory 17B. Main memory 17B is a relatively fast memory. A typical access time is in the range from 20 to approximately 400 nanoseconds. Access time is the time interval between when CPU 10 requests data from memory 17 and when memory 17 makes the requested data available to CPU 10.
Mass memory 17A is usually used to store programs not being executed and data not being accessed and, because of size limitations of main memory 17B, is also frequently used to store at least a portion of the program currently being executed by CPU 10 and data required by this program. Mass memory 17A is significantly slower than main memory 17B. Access time for mass memory is typically on the order of tens of milliseconds.
A computer system which can be connected to a disk drive typically utilizes a disk drive controller chip which receives data, addressing, and other control lines from the microprocessor and coordinates data transfers to and from the disk drive. The disk controller typically performs a number of functions, including automatic verification, format compatibility, read or write with simple or multiple blocks, automatic sector search, complete track read or write, and simultaneous control of several disk drives.
The disk controller chip is mounted within the housing of a typical portable computer which also encloses the microprocessor, memory, and support circuitry. The disk controller may be connected to a cable which extends out of the computer housing to a disk drive if the disk drive is not included within the computer housing.
With the increasing use of computers in modern-day society, there has developed a demand for battery powered computers which can be transported from location to location without burden and which can be operated in virtually any location
However, most battery powered computers available today have several limitations. Primary limitations include lack of computing power and memory space. Most battery powered computers are not capable of running the same programs as can be run on popular, modern, desk top PCs, such as the IBM PC/XT. The inability of battery powered computers to run the same programs as their contemporary desk-top counterparts has resulted in slow acceptance and minimal use of battery powered computers.
A few battery powered computers have been developed which use the same microprocessors and have the same memory capacity as popular desk top PCs. Many of these battery powered computers, however, have extremely short battery lives and require specialized battery packs. In addition, they are relatively large and some do not provide convenient connection to external disk drives.